Is there a command to know what software is currently either handling/managing the network?

Shell Scripting & Linux Command Line
21

Just been playing with nmcli today…

Got some RHEL9 servers hosted in AWS EC2 that get their DHCP lease from “some thing” on their VLAN… They’re replacing some RHEL7 servers I recently configured to use static “host assigned” IP addresses (simple as editing /etc/sysconfig/network-scripts/ifcfg-$NIC files) instead of DHCP…

I need to change their (the RHEL9) DNS settings… Apparently it has to be done on the VPC for everything using that VPC… But I don’t want to do a global change.

Found some “nmcli” command strings that I can use (I tested them on a VirtualBox RHEL9 instance)… Those config changes survive reboots… phew!

Everything’s becoming WAY more complex than it needs to be…

Excerpt from my shell history on that VirtualBox RHEL9 instance :

   63  sudo nmcli connection modify enp0s3 ipv4.dns "8.8.8.8 8.8.4.4"
   68  sudo nmcli connection mod enp0s3 ipv4.ignore-auto-dns yes
   71  man nmcli
   72  sudo nmcli connection mod enp0s3 ipv4.dns-search saturno.net

And to enforce each change sudo systemctl restart NetworkManager (there’s probably a better way - but at least your session doesn’t disconnect) - but after restarting NetworkManager SystemD - I can see my changes in /etc/resolv.conf (why can’t we edit that file directly? What a bullshit backwards step that is!)

[root@rel9-000 ~]# cat /etc/resolv.conf
# Generated by NetworkManager
search saturno.net
nameserver 8.8.8.8
nameserver 8.8.4.4
nameserver fe80::da44:89ff:feee:c453%enp0s3

In Australia (or even Blighty) when we see bullshit like this we’d exclaim : “surely they’re taking the piss!”… Why? Was that easier?

That :
# Generated by NetworkManager
Is a dire warning - it’s not stated - but implied “DO NOT EDIT THIS FILE”…

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22

DANG!

It gets even uglier when you get down to brass tacks!

So - “ip a” shows me that my NIC is called “eth0” so you’d a thunk that’s the device you need to manage with nmcli - but - you’d be WRONG!

2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 9001 qdisc mq state UP group default qlen 1000
    link/ether REDACTED brd ff:ff:ff:ff:ff:ff
    altname enX0
    inet REDACTED brd REDACTED scope global dynamic noprefixroute eth0
       valid_lft 3179sec preferred_lft 3179sec
    inet6 REDACTED scope link
       valid_lft forever preferred_lft forever

To get the NetworkManager name of the “connection” you need to :

[root@hcausinft01 NetworkManager]# nmcli con show
NAME         UUID                                  TYPE      DEVICE
System eth0  5fb06bd0-0bb0-7ffb-45f1-d6edd65f3e03  ethernet  eth0
lo           db7605c1-c591-4ea1-9677-c2cc89111432  loopback  lo

And guess what? The “NAME” has a space in it - WTF?
So to mod the connection - you need something like :
nmcli connection mod "System eth0" ipv4.ignore-auto-dns yes

The only file I can find that it updated (on restarting Network Manager) was /etc/resolv.conf… I can’t find ANY updated files in /etc/NetworkManager, the folder /etc/NetworkManager/system-connections is empty and “NetworkManager.conf” is all commented out and hasn’t been touched or modified for months… In fact NONE of the subfolders in /etc/NetworkManager/ have any files in them… This bullshit is like that abomination The Windows Registry crap! ZERO FILES have been updated in /etc/NetworkManager for weeks / months!

WHERE DOES IT READ THE CONFIGURATION FROM??? Note : above is RHEL9 - so not Netplan…

Apparently - you can enable a “plugin” on RHEL9 “ifcfg-rh” that will read configurations from /etc/sysconfig/network-scripts/ - but I already figured out how to do it with nmcli… In fact - on the above RHEL9 system - there is a /etc/sysconfig/network-scripts/ifcfg-eth0 - but the top header of the file :

# Created by cloud-init automatically, do not edit.
#

Stuff of nightmares!
– EDIT –
Above examples were RHEL9 hosted in AWS EC2.
My VirtualBox VM of RHEL9 doesn’t have “cloud-init” and my changes get saved where I’d expect them : /etc/NetworkManager/system-connections/

I’m using DHCP :

[root@rel9-000 system-connections]# cat enp0s3.nmconnection 
[connection]
id=enp0s3
uuid=3872190a-0832-370c-9e0d-0fea043d4037
type=ethernet
autoconnect-priority=-999
interface-name=enp0s3
timestamp=1742450235

[ethernet]

[ipv4]
dns=8.8.8.8;8.8.4.4;
dns-search=saturno.net;
ignore-auto-dns=true
method=auto

[ipv6]
addr-gen-mode=eui64
method=auto

[proxy]

And it doesn’t have some dodgy name with a space - it’s just “enp0s3”…

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